When cornering, a vehicle and the occupants are subjected to lateral (or centrifugal) acceleration directly proportional to the square of vehicle speed, and inversely proportional to the curve radius.
Lateral acceleration of an occupant of a vehicle when cornering results in a lateral force which tends to push the occupant out of the seat. Which is why vehicle seats normally provide for a certain degree of lateral restraint to counteract the lateral forces to which occupants are subjected when cornering.
When driving normally along public highways, vehicle speed, and therefore lateral acceleration when cornering, are relatively low, so that vehicle seats need only a minimum amount of lateral restraint to ensure adequate driving comfort of the occupants. Conversely, when racing on track or along highways closed off to the public, vehicle speed is high, so that lateral acceleration when cornering may reach extremely high levels (as much as 1 g in the case of sports cars). In which case, the seats offer a high degree of lateral restraint to prevent the occupants from being unseated when cornering. It should be pointed out that a seat with a high degree of lateral restraint serves not only to prevent undesired lateral movement of the driver when cornering, but also to transmit any lateral stress promptly to the driver's body, to enable the driver to “physically feel” the dynamic performance of the vehicle.
In the case of a sports vehicle that can be used both normally on public highways and on race tracks, a trade-off in terms of the degree of lateral restraint of the seats is inevitable. That is, it should not be so low as to penalize racing performance, but at the same time it should not be so high as to impair easy access to the seat portion of the seat during normal use. The compromise struck normally fails to achieve either. The only valid alternative is to have two sets of seats, one for normal use, and one for racing. Changing the seats, however, is a fairly long, painstaking job which calls for skilled labor, in that incorrect assembly may have serious consequences, particularly in the event of accidents.
Moreover, a seat with a high degree of lateral restraint fails to comfortably accommodate occupants of different build—and is therefore adapted to the build of the usual occupant—and makes entering and exiting the vehicle particularly awkward. These drawbacks are obviously routine in track racing, but are unacceptable during normal use of the vehicle.
German Patent Publication No. DE10211383, which is incorporated herein by reference, discloses a vehicle seat having a mechanical shaping mechanism, which comprises a memory metal and is controlled by an evaluation unit connected to force sensors arranged in the seat.